The space elevator will be built about 50 years after everyone stops laughing.

No communication technology has ever disappeared, but instead becomes increasingly less important as the technological horizon widens.

Good morning, Dr. Chandra. This is Hal. I am ready for my first lesson.

Astronomy, as nothing else can do, teaches men humility.

He was moving through a new order of creation, of which few men had ever dreamed. Beyond the realms of sea and land and air and space lay the realms of fire, which he alone had been privileged to glimpse. It was too much to expect that he would also understand.

I also believe - and hope - that politics and economics will cease to be as important in the future as they have been in the past; the time will come when most of our present controversies on these matters will seem as trivial, or as meaningless, as the theological debates in which the keenest minds of the Middle Ages dissipated their energies. Politics and economics are concerned with power and wealth, neither of which should be the primary, still less the exclusive, concern of full-grown men.

Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living.